ABCG1 is a cholesterol transporter involved in the efflux of cholesterol to HDL in reverse cholesterol transport. In the prior funding period, we discovered that mouse models of Type 2 diabetes as well as human subjects with Type 2 diabetes have decreased ABCG1 expression and function. We also uncovered an important intracellular role of ABCG1 and sterols in regulation of T cell proliferation and activation. We will extend these fundings in this new funding period to study how T cell homeostasis and activation are changed during atherosclerosis progression as well as in Type 2 diabetes. We will use a combination of studies in mice and in humans to address these questions. In collaboration with Project 3, (McNamara), we will study how Id3 regulates Tregulatory (Treg) phenotypes; in collaboration with Project 2 (Miller), we will examine how oxidized lipids influence Treg and monocyte phenotypes in atherogenesis. We will also obtain blood samples from the Human Phenotyping and Immune Cell Core to measure the cholesterol content and inflammatory phenotype of T cells isolated from subjects with atherosclerosis and/or with Type 2 diabetes. We will correlate these T cell measurements with clinically measured parameters for atherosclerosis and type 2 diabetes, such as carotid artery intima-media thickness (CIMT), hemoglobin Ale (HbAlc), and plasma lipoprotein levels. This project is directly related to the PPG theme of uncovering mechanisms contributing to the immunobiology of atherosclerosis.